As already suggested, this is your trip, and as such, it needs to be your choice as to where you go and what you see. So far we do not know much about you, other than that you want to take your camper and do the coast road in the West.

Like Donna, I suggest that you start with choosing the sights you wish to see, rather than the route you wish to travel. For example, if you are interested in spending some time in Yellowstone NP, then you could take the I-90 if you also wanted to see Badlands. On the other hand, you'd be more inclined to take I-80 if northern CO or Salt Lake City were of more interest to you.

Once you have some dots on the map, be sure to come and ask more questions, and the experts here will help you fine tune your trip and make further suggestions along the way.

Enjoy the planning.

Lifey